As industrial society has been being partially transformed into an advanced information age, the importance of electronic displays as a medium for displaying and transferring various pieces of information is increasing day by day. Conventionally, a bulky CRT (Cathode Ray Tube) was widely used therefor but faces considerable use limitations as a result of the space required to mount it, thus making it difficult to manufacture CRTs of larger sizes, and accordingly CRTs are being replaced with various types of flat panel displays, including liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), and organic electroluminescent displays. Among such flat panel displays, LCDs in particular are technologically intensive products resulting from a combination of liquid crystal-semiconductor techniques and are advantageous because they are thin and lightweight and consume little power. Therefore, research and development into structures and manufacturing techniques thereof is continuing. Nowadays, LCDs, which have already been applied to fields such as notebook computers, monitors for desktop computers and portable personal communication devices (PDAs and mobile phones), are being manufactured in larger sizes, and thus it is possible to apply LCDs to large-sized TVs such as HD (High-Definition) TVs. As a result, LCDs are receiving attention as novel displays able to substitute for CRTs, which used to be synonymous with displays.
In LCDs, because the liquid crystals themselves cannot emit light, an additional light source is provided at the back surface thereof so that the intensity of light passing through the liquid crystals in each pixel is controlled to realize contrast. More specifically, the LCD, serving as a device for adjusting light transmittance using the electrical properties of a liquid crystal material, emits light from a light source lamp mounted to the back surface thereof, and the light thus emitted is passed through various functional prism films or sheets to thus cause light to be uniform and directional, after which such controlled light is also passed through a color filter, thereby realizing red, green, and blue (R, G, B) colors. Furthermore, the LCD is of an indirect light emission type, which realizes an image by controlling the contrast of each pixel through electrical methods. As such, a light-emitting device provided with a light source is regarded as important in determining the quality of the image of the LCD, including luminance and uniformity.
Such a light-emitting device is mainly exemplified by a backlight unit (BLU). Typically, light emitted from a plurality of light sources including a cold cathode fluorescent lamp is sequentially passed through a diffusion plate, a diffusion sheet and a prism sheet, and then reaches a liquid crystal panel. The diffusion sheet plays a role in realizing uniform light intensity over the entire front surface of a screen and simultaneously performs a hiding function so that a device such as the light source mounted under the diffusion sheet is not visible from the front surface. The prism sheet functions to control the light path so that light rays directed in various directions having passed through the diffusion sheet are transformed within a range of viewing angles θ suitable for enabling the image to be viewed by an observer.
In the course of diffusing the light emitted from the light sources using the diffusion sheet and collecting such diffused light using the prism sheet, however, it is possible to collect only the light which is incident within a predetermined angular range. Thus, as part of the light which is not collected is reflected back from the prism sheet or generates sidelobes, the loss of light occurs, undesirably resulting in reduced luminance.
Also, an LCD is recently manufactured to be lightweight and slim and have low power consumption in order to satisfy the demands of consumers. One method of manufacturing an LCD to be slim includes reducing the thickness of the BLU which is an essential element of the LCD. However, the BLU includes a plurality of sheets for increasing the efficiency of light so that light reaches the liquid crystal panel and thus inevitably has a certain degree of thickness. Accordingly, limitations are imposed on reducing the thickness of the LCD to below a predetermined level. Moreover, when the distance between the light source and the sheet is shortened to decrease the thickness of the BLU, hiding performance is reduced. Further, deformation of the sheet may be caused by extended exposure to heat. Hence, attempts to decrease the number of sheets which are mounted in the BLU have been made, but the degree of reduction of the thickness of the BLU thereby has not been large.
On the other hand, support pins are provided between the plurality of light sources to hold the diffusion plate disposed on the light sources. In the case where the light sources are in an on-state for a long period of time and then turned off or are maintained in an off-state and then turned on, the diffusion plate may expand and then shrink or may expand too quickly, due to the change in temperature. If so, the support pins used for holding the light sources may be pulled by the change in the diffusion plate, undesirably causing problems in which the diffusion plate is scratched or noise occurs. In particular, when the distance between the light source and the diffusion plate is shortened to reduce the thickness of the BLU in order to manufacture a slim LCD in accordance with the demands of consumers, the diffusion plate is greatly affected by the change in temperature depending on the state of the light source. In this case, as the distance between the support pin and the diffusion plate is also shortened, the probability of generating friction or noise due to the change in temperature may be further increased.
Hence, there is a need for the development of a member which minimizes the loss of light, enables light rays in the wider angular range to be collected forwards to efficiently increase luminance, exhibits high heat resistance while realizing hiding performance after reducing a distance between a light source and a sheet equal to or higher than hiding performance before reducing a distance between a light source and a sheet, and prevents problems from occurring as a result of friction between a diffusion plate and a support pin attributable to expansion and shrinkage of the diffusion plate.